Osseointegrated implants have been developed as the result of the discovery of the ability of bone to make direct biological attachment to the surfaces of titanium implants. (See Dental Implants: Tissue-Integrated Prosthesis Utilizing the Osseointegration Concept" published in the Mayo Clinic Proceedings, vol. 61 February 1986, pp 91-97). An example of osseointegrated implants is osseointegrated dental implants used as an alternative to a single tooth, fixed bridge or removable dentures to form a final restoration. The procedure involves a first operation to surgically expose the bone and, to drill a hole in the bone where an implant, for example, a titanium anchor element, is to be inserted. An implant having a central aperture temporarily blocked by a covering plug is inserted into the drilled hole in the bone. A flap of skin is then sewn over the site. During the healing period, the bone tissue becomes biologically attached to the titanium implant by growth of the bone tissue.
After the implants have become biologically attached to the bone, the top surfaces of the implants are exposed in a second operation. Sometimes, a metal abutment or "spacer" is attached to each implant as an intermediate between the implant and the framework of the prosthesis, for example when there is a space between the patient's jawbone and the gum tissue above. The description that follows refers to the use of an abutment or spacer.
In order to achieve the desired arrangement of the prosthetic teeth on the implants in the final restoration, a negative impression is made of the patient's mouth which includes the implant sites, and any remaining teeth and gums. One method for making a negative impression involves attaching a temporary stud or a coping to each implant in place of the covering plug. An impression material contained in a dental impression tray is applied around the copings and the dental process. After the impression material cures, the tray with the impression material is then removed from the patient's mouth. The copings are either embedded in the impression material when it is removed from the patient's mouth or reinserted into the impression material after the impression material is removed from the patient's mouth. U.S. Pat. No. 4,693,683 to Lee and U.S. Pat. No. 4,432,728 to Sharkey describe dental trays and techniques for making impressions.
Another method for making a negative impression of the dental process is disclosed in U.S. Pat. No. 5,055,047 to Names. Names discloses a metal impression confirmation system for making an accurate impression for preparing an implant supported dental prosthesis. Individual foundation elements, which are affixed to adjacent elements with a bonding resin, are used to form a rigid metallic framework. An impression is taken of the framework and gums and any remaining teeth. The rigid metallic framework helps to minimize or prevent distortion of the impression material as it cures, and also to prevent distortion of the poured stone for the master model while it cures, to ensure a more accurate molded impression. After the impression material sets, the tray with the impression material and the framework, is then removed from the patient's mouth.
An abutment analog with an aperture and a top surface corresponding to the aperture and the top surface of the abutment attached to the implant is temporarily attached to each coping or foundation element embedded in the negative impression. A positive master stone cast model of the patient's mouth can then be made from the negative impression by embedding the abutment analogs into a material such as gypsum and removing the negative impression by unscrewing the copings or the foundation elements from the abutment analogs. This results in a master stone model that duplicates the location of the implants in the patient's mouth. The positive master model ensures that the prosthesis will match the top of the implants (with or without abutments attached) when the prosthesis is inserted onto the implants in the patient's mouth.
Caps may then be attached to the abutment analogs embedded in the master positive model and a bridge body wax model on the caps, reinforced by a supporting plastic plate, is then produced. The bridge body wax model (the bite template) is placed in the patient's mouth and the caps are screwed onto the abutments. This step checks the accuracy of the impression and determines the height of the bite and the shape of the tooth curvature. After returning the bite template to the master positive model, the positive master model is matched to a positive master model of the opposite jaw and the two positive master models are mounted in an articulator.
In the bite template, teeth of plastic material (acrylate) matching the teeth of the opposite jaw, if any, are attached. The bite template with the teeth is tested in the patient's mouth and then is returned to the master positive model in the articulator. After the positions of the teeth are determined by pre-molding the teeth in soft plastic material, the teeth are removed from the bite template. New wax, connecting the caps on the bite template and built to a suitable dimension, and the caps are then embedded into gypsum. The new wax is melted and removed from the gypsum mold and molten cast gold is poured into the gypsum mold cavity, the caps being embedded into the gold as it sets.
The gold bridge body is removed from the gypsum mold and secured via the caps to the abutment analogs of the master positive model in the articulator. The teeth, the positions of which had been determined by the soft plastic pre-molding, are then attached to the gold bridge body by means of wax. The connection of the gold bridge body to the abutments via the caps is tested in the patient's mouth. If the fit is acceptable, the wax retaining the teeth to the gold bridge body is replaced by plastic material (acrylate) which permanently attaches the teeth to the gold bridge body by means of a pressing method. The gold bridge body with teeth is then screwed onto the abutments attached to the implants via the caps molded in the gold bridge body.
The entire process for preparing a final restoration as described above using fixed implants and a prosthesis involves numerous steps and materials and is tedious and time-consuming. Accordingly, there remains a need in the art for an improved system and method which simplifies the overall process by eliminating some of the steps and materials and thereby decreases the time and cost requirements for preparing the final restoration.
There remains a further need in the art for a system and method for accurately establishing the locations and orientations of the implants and preserving the accuracy throughout the entire process of preparing a final restoration.
There remains yet a further need in the art for a system and method for providing a foundation onto which a removable or fixed prosthesis is attached that is simple to roduce, and is readily adjusted to confirm the fit of the prosthesis on the fixed implants.